simple difference from what-is-difference-Application-Architecture-and-Design-Patterns
Application Architecture describes the structure and behavior of applications used in a business. It focuses on how these applications interact with each other and with users. It focuses on the inputs and outputs of applications rather then there internal structure. The applications architecture is specified on the basis of business requirements. It involves defining the interaction between application packages, databases, and middleware systems in terms of functional coverage. Application architecture is at a more abstract level and is independent of the implementation.
Design Patterns are the guidelines to avoid/solve common problems in application development. Design patterns tell us how we can achieve a solution in terms of implementation. Design patterns are independent of the programming language and technology platform i.e. we can implement a particular design pattern in any language.